For a run flat traveling of a vehicle at the emergent situation such as a puncture or the like, it is useful to equip at the inside of the pneumatic tire with a core attached to a rim.
The core comprises a ring-shaped supporting member (metal annular body, sometimes, “shell”) which is generally formed of a plate-like member and which supports the pneumatic tire by allowing the inside of a tread portion of the tire to be brought into contact with an outer peripheral surface of the supporting member at the time of the pneumatic tire deformation due to an internal pressure decrease of the tire, and ring-shaped rubber portions which are vulcanized and joined respectively to both edge portions in a widthwise direction (hereinafter, “both widthwise direction edge portions”) of the supporting member. When such a core is manufactured as a product, after manufacturing the supporting member in advance, the supporting member and the rubber portions are joined to each other by using a dye.
For example, there are four manufacturing examples: Manufacturing Example 1 (bladder vulcanizing method): pre-molded unvulcanized rubber members are disposed at the both widthwise direction edge portions of the supporting member, the unvulcanized rubber members and the supporting member are set in a die, pressurized from the inner surface side of the supporting member with the bladder, further heated, and vulcanized to manufacture a product.
Manufacturing Example 2 (compression molding and vulcanizing method): pressurization technology described in Japanese Patent Application (Laid-Open) No. 48-021765 is utilized in which the supporting member is set in a compression molding die, and the widthwise direction side portions of the supporting member are compression-molded simultaneously, and vulcanized to manufacture a product (see FIG. 9).
Manufacturing Example 3 (injection molding and vulcanizing method): injection technology described in JP-A No. 62-032038 is utilized in which the supporting member is set in an injection molding die. Rubbers are injection-molded sequentially at both edge portions of the supporting member, and then vulcanized to manufacture a product.
Manufacturing Example 4 (transfer molding and vulcanizing method): transfer technology described in JP-A Nos. 62-240519 and 04-267117 is utilized in which the supporting member is set in a transfer molding die. Rubbers are injection-molded sequentially at both edge portions of the supporting member, and then vulcanized to manufacture a product.
However, there have been arisen the problems as described below:
In the bladder vulcanizing method, an adhesive is applied onto the surface of the supporting member for a purpose of a joint between the supporting member and the rubber portions thus adherence between the bladder and the supporting member may occur. For this reason, the bladder is noticeably deteriorated making it necessary to replace the bladder with every completion of about 10 products' processing.
In the compression molding and vulcanizing method, when the supporting member is simultaneously compressed in a vertical direction by using a lower die and an upper die, rubber material must be preset at the lower die. For this reason, grooves to be inserted into the rubber material must be preformed at the supporting member or the rubber material must be divided into two members thus requiring for another step for presetting. At this point, the presetting becomes unnecessary by raising a core portion for supporting the supporting member and by setting the rubber material beneath the supporting member. In this case, however, the supporting member may deform or the product size may change.
In the injection molding and vulcanizing method, because the both edge portions of the supporting member are molded sequentially, vulcanization molding must be performed twice thus leading to a prolonged manufacturing time for one product resulting in less productivity. Further, a rubber extruder becomes necessary. Therefore, in order to simultaneously mold the rubber portions at the both widthwise direction edge portions of the supporting member, the equipment or the die becomes complicated resulting in a boost of the equipment cost, which is not preferable.
Being different from the injection molding and vulcanizing method, in the transfer molding and vulcanizing method, the extruder is unnecessary. However, since the both edge portions of the supporting member are molded sequentially thus leading to a prolonged manufacturing time for one product resulting in less productivity.